He was born in Edinburgh in 1707, the son of Rev James Webster, second charge of Tolbooth parish in St Giles Cathedral and a covenanting minister, originally from Fife.
The tables which he drew up from information obtained from all the presbyteries of Scotland were based on a system of actuarial calculation that supplied a precedent followed by insurance companies in modern times for reckoning averages of longevity.
[2] Webster published in 1748 his Calculations, setting forth the principles on which his scheme for widows' pensions was based; he also wrote a defence of the Methodist movement in 1742, and Zeal for the Civil and Religious Interests of Mankind Commended (1754).
In 1771 he was appointed a Dean of the Chapel Royal and Chaplain in Ordinary to George III in Scotland.
[5] Socially, despite his 'High Flying' Evangelical position in the Kirk, he was a convivial man, known as Bonum Magnum for his capacity for claret.